A continuous regeneration type diesel particulate filter (hereinafter referred to as the “DPF”) apparatus is an exhaust emission purification apparatus which accumulates particulate matter (hereinafter referred to as the “PM”) emitted from a diesel engine by the DPF.
In the continuous regeneration type DPF apparatus, the PM accumulated by the DPF is continuously combusted and purified when the temperature of exhaust gas is at least about 350° C. Thus the DPF is self-regenerated. If, however, the exhaust gas temperature is low under a low speed driving and low loading condition or the like, the catalyst temperature becomes low and the catalyst is not activated, which results in difficulty in oxidizing the PM and self-regenerating the DPF. As a result, clogging of the DPF proceeds caused by the deposition of PM in the DPF, thereby raising a problem of exhaust pressure increase by the clogging.
If the amount of PM deposited in the DPF exceeds a predetermined value (a threshold value), forced regeneration is executed to forcefully combust to remove the entrapped PM by forcefully raising the temperature of exhaust gas by applying multistage delayed injection (multiple injection), post-injection, and the like in the cylinder. The forced regeneration combusts hydrocarbons (HCs), which are supplied to the exhaust gas by the post-injection or the like, using an oxidation catalyst positioned at upstream side of the DPF or an oxidation catalyst supported on the DPF. Whereby, by utilizing the oxidation reaction heat, the exhaust gas temperature at inlet of the DPF and on the filter surface of the DPF is raised, thereby raising the DPF temperature to at least a level that the PM accumulated in the DPF combusts. By the temperature raising, PM is combusted and removed.
The forced regeneration is executed either by manual regeneration or by automatic regeneration. For the case of manual regeneration, an alarm is generated to the driver when the clogging of DPF exceeds a predetermined value. On receiving the alarm, the driver presses a button for starting the forced regeneration to execute the forced regeneration. On the other hand, in the automatic regeneration, the forced regeneration is executed even during automatic driving when the clogging of filter exceeds a predetermined value without specifically generating alarm to the driver.
According to the forced regeneration, the vehicle is in the stopping state, even for the automatic regeneration, in the cases that the forced regeneration is executed when an idling state continues for a predetermined period or longer, and that the driving state at the beginning of the forced regeneration enters the vehicle stopping state. Furthermore, according to the forced regeneration, the vehicle is in the stopping state in the case of manual regeneration when the driver stops the vehicle and presses the switch of forced regeneration. Regarding the forced regeneration in the vehicle stopping state, there is a case of executing control by closing the exhaust throttle valve (exhaust brake valve or exhaust throttle valve) to increase the engine load to hold the temperature of DPF.
For example, Japanese Patent Application Kokai Publication No. 2005-139992 (paragraph [0040]) discloses a regeneration control, as described below, in an exhaust purification apparatus provided with a means for supplying fuel at upstream side of the DPF. According to the apparatus, regeneration control is given by increasing the idling rotational speed from the normal speed at the fuel-supply time in the idling state. In the regeneration control, the amount of exhaust flow is reduced through closing a means for throttling exhaust such as exhaust brake. By the action, the exhaust resistance increases to make the inflow of intake air of relatively low temperature into the cylinder difficult, thereby increasing the amount of remained exhaust gas at a relatively high temperature. The air in the cylinder containing relatively large amount of the exhaust gas at a relatively high temperature, is compressed in the succeeding compression step to enter the explosion stage, which attains further raising the exhaust gas temperature.
In addition, for example, Japanese Patent Application Kokai Publication No. 2005-282545 proposes an exhaust emission purification system executing control of an exhaust throttle valve, as described below, during operation of a means for raising exhaust gas temperature at the time of small entrapping amount using a multiple injection (multistage delayed injection) of the DPF forced regeneration. That is, in the driving state, the exhaust throttle valve (exhaust brake valve or exhaust throttle valve) is opened, and for the case of transition from the driving state to the vehicle stopping state, the exhaust throttle valve is closed, and further in the case of transition from the vehicle stopping state to the driving state, the exhaust throttle valve is closed.
In these cases, however, there arise following-described problems. During forced regeneration in the vehicle stopping state, there are cases of increase in the engine load in a refrigeration vehicle, for example, by starting the compressor of refrigerator. At the time of increase in the engine load, if the exhaust throttle valve is closed, fresh air is difficult to enter the engine cylinder so that the amount of intake air decreases to deteriorate the combustion in the cylinder.